Bleaching and filling leather with amino carboxylic acid-methylol melamine resin



Patented Apr. 24, 1951 BLEACHHNG AND FILLING LEATHER- WITH AMINOCARBOXYLIC ACID-METHYLOL T/IELAIVHNE RESIN William 0. Dawson, Stamford,Conn, assignor to American Cyanamid Company, New York, N. Y., acorporation of Maine No Drawing.

Application August 25, 1945,

Serial No. 612,710

4 Claims. 1

This invention relates to a method of finishing leather by impregnatingit with a novel class of finishing agent having bleachin and fillingproperties. More particularly, the invention relates to the treatment ofvegetable, mineral or resin-tanned leather with water-soluble orwaterdispersible finishing compositions containing condensation productsof methylol melamines with aminocarboxylic acids.

In my Patent No. 2,316,741 dated April 13, 1043, I have shown thatmethylol melamines are excellent tanning and finishing agents for hides,skins, and leather. I have now discovered that water-dispersibleproducts having good bleaching and filling properties for leather areobtained when methylol melamines are condensed with aminocarboxylic acidsalts. These condensation products form stable aqueous solutions whichcan be shipped to and stored by the customer without deterioration, andwhich can be added directly to leather finishing processes.

Although the present invention is not limited to condensation productsof definite structure, I have found that certain well-defined com-poundsare obtained by condensing monomeric or partially polymerized methylolmelamines containing 1 or more free methylol groups with watersolublesalts of aminocarboxylic acids of the aromatic and aliphatic series;such as the alanines, glycocoll, beta-aminebutyric acid and other aminofatty acids, as Well as anthranilic acid, para-aminobenzoic acid, andother aminocarboxylic acids of the aromatic series. Thecondensationreaction which takes place is illustrated by the following equationwherein the symbol M represents a methylol melamine, either in themonomeric or in a partially polymerized condition, R is the residue ofan aminocarboxylic acid of the aromatic or all-- phatic series and istherefore an aryl or alkylene radical, and X is a salt-forming radicalsuch as sodium, ammonium, ethanolamine and the like.

Although compounds of definite composition can be obtained by condensingequiinolecular quantities of a methylol melamine and a salt of anaminocarboxylic acid, as indicated by the above equation, the inventionis not limited to compounds of definite composition. on the contrary, Ifind that stable solutions possessing bleaching and filling propertiesfor leather are obtained when considerably less than the theoreticalquantities of aminocarboxylic acid are employed. Thus, for example, Ihave obtained bleaching and filling compositions of good stability byreacting anywhere from 1 to 2 mols of a methylol melamine with 1 mol ofan aminocarboxylic acid, and in some cases the ratio may even be as highas 2.1:1. This permits an important saving in the cost of the bleachingand filling compositions of the invention, since the aminocarboxylicacid is usually more expensive than the methylol melamine.

The condensation products used in practicing the process or" the presentinvention are preferably obtained by adding an aqueous solution ordispersion of the methylol melamine to a water solution of awater-soluble saltof the aminocarboxylic acid followed by heating themixture at temperatures of about 30 to 100 C., or up to the boilingpoint of the solution. The reaction product is obtained as a clear,aqueous solution which can be diluted with water to the concentrationdesired for the tanning or bleaching of leather.

When a composition of improved stufiing or filling properties is desiredit is usually preferable to heat the clear solution of the condensationproduct at a pH of about 5-7 to promote further polymerization, so thata solution of increased viscosity is obtained. By polymerizing thecondensation product in this manner its filling properties areconsiderably improved. For greater stability on storage an alkali suchas borax or sodium hydroxide is preferably added in amounts suflicientto raise the pH to about 9-11 after polymerizing to the desired degree.

The methylol melamine-aminocarboxylic acid condensation products may beapplied to the leather by any suitable process; however, I prefer toapply them in a tanning drum by the methods described in my earlierpatent referred to above. The condensation products are preferablyapplied to the leather as an aqueous solution containing 110% of thecondensation product, although for special purposes stronger solutionsmay be employed. Finishing processes requiring complete penetration ofthe condensation product are usually carried out at relatively highdilutions of th condensation product and for considerably longer periodsof time than are bleaching processes in which the principal object is toobtain a lightening of the color of the leather. After the leather hasbeen impregnated with the condensation product to the desired de gree itis usually washed with water and may be fatliquored by an suitableprocedure, such as by an aqueous emulsion of neatsfoot oil.

The invention will be further illustrated by Example 1 To 37.5 grams ofglycine add grams of so dium hydroxide and 230 grams of water. To theclear solution add 126 grarns of melamine and 284 grams of 37% aqueousformaldehyde. Heat at 50-55 C. until a clear solution is obtained.Dilute hydrochloric acid is added, if necessary, to adjust the pH to6.0-7.6. The mixture is heated until the desired viscosity is obtained.Alkali is then added to adjust the pH to 9.011.0 and water then added todilute the solution to 20% solids. This solution is stable duringshipment and storage and is an excellent bleaching agent for chrometanned leather.

Example 2 A solution of sodium p-aminobenzoate is prepared by'dissolving 68.5 grams of p-aminobenzoic acid and 100 grams of a 20sodium hydroxide solution in 185 grams of water. 126 grams of melamineand 284 grams of 37% aqueous formalin are then added and the mixture isheated with agitation at 50-55 C. until a clear solution is obtained.The pH is then adjusted to 6.0 and 1 heating is continued until thedesired viscosity is obtained. When a filling and bleaching agent forchrome tanned leather is desired the viscosity is usually carried to ahigher degree than when the compound is to be used for tanning.Sufficient alkali is then preferably added to raise the pH of thefinished solution to 9-11 after which it is diluted to 20% solids.

Erample 3 50 grams of 20% sodium hydroxide solution and 44.5 grams ofbeta-alanine are dissolved in 200 grams of water to a clear solution.

A trimethylol melamine solution is prepared by dissolving 126 grams ofmelamine in 284 grams of 37% aqueous formaldehyde solution, neutralizedwith sodium hydroxide to a pH of 7-3, at a temperature of G0-70 C.,followed by cooling.

The two solutions are mixed and heated at 50-55 C. until no turbidityremains, after which the pH may be adjusted to 6 and heating con--tinued if a solution of higher viscosity is desired. Increased storagestability is obtained by adding sufiicient borax or caustic soda toraise the pH to 9-10, after which the product may be diluted with waterto any desired concentration for use.

Example 4 pounds of chrome tanned kipskins (six skins) were suspended inwater at F. and 2% of sodium acetate, based on the dry weight of theskins, was added. After drumming 20 minutes, draining, and againdrumming 5 minutes with fresh water and draining, the leather wassuspended in water in a tanning drum at F. and 10% of the solution ofExample 1 (20% solids) was added. The drum was then rotated for 1 hour,after which the leather was drained, washed with water fatliquored andpigmented and horsed up over night. The next morning the leather was setout and dried. In this cordition it was full and tight and considerablylighter and of better color than regular chrome tanned leather.

What I claim is:

1. A method of bleaching and filling leather which comprisesimpregnating the leather with an aqueous solution of the polymerizedcondensation product of 1 mol of an aminocarboxylic acid with 1-2.5 molsof a methylol melamine.

2. A method according to claim 1 in which the aminocarboxylic acid is analiphatic amino'carboxylic acid.

3. A method according to claim 2 in which the aliphatic aminocarboxylicacid is glycocoll.

4. A method of bleaching and filling leather which comprisesimpregnating the leather with an aqueous solution of the polymerizedcondensation product of one mol of an aromatic aminocarboxylic acid with1 to 2.5 mols of a methylol melamine.

- WILLIAM O. DAWSON.

REFERENCES CITED The following references are of record in the

1. A METHOD OF BLEACHING AND FILLING LEATHER WHICH COMPRISESIMPREGNATING THE LEATHER WITH AN AQUEOUS SOLUTION OF THE POLYMERIZEDCONDENSATION PRODUCT OF 1 MOL OF AN AMINOCARBOXYLIC ACID WITH 1-2.5 MOLSOF A METHYLOL MELAMINE.